1. Field of the Invention
This invention relates to a control apparatus and a control method applied to an internal combustion engine including a turbocharger, with which an opening of a wastegate valve provided in an exhaust gas bypass passage is controlled using an electric actuator.
2. Description of the Related Art
An internal combustion engine including a turbocharging device such as a turbocharger has been put to practical use conventionally with the aim of improving output. Note that a turbocharger is a device that compresses intake air supplied to an internal combustion engine main body by rotating a turbine using energy from exhaust gas and driving a compressor connected to the turbine.
Further, in a well-known technique applied to an internal combustion engine having a turbocharger, an exhaust gas bypass passage that bypasses the turbine is provided in an exhaust gas passage of the internal combustion engine, and a wastegate valve is provided in the exhaust gas bypass passage.
By adjusting an opening of the wastegate valve, a flow rate of the exhaust gas flowing through the exhaust gas bypass passage, or in other words the flow rate of the exhaust gas flowing into the turbine, is adjusted, and as a result, the pressure of the intake air compressed by the compressor that rotates integrally with the turbine is controlled. The pressure of the intake air compressed by the compressor will be referred to hereafter as a supercharging pressure.
Furthermore, to realize a desired supercharging pressure corresponding to operating conditions of the internal combustion engine, a control apparatus applied to an internal combustion engine having a turbocharger determines a target opening of the wastegate valve and performs feedback control so that an actual opening of the wastegate valve, detected by a position sensor, matches the target opening.
However, it is known that due to individual differences and temporal variation in respective component characteristics of the turbocharger, the wastegate valve, and driving systems thereof, as well as temperature variation and so on, a difference may occur in the actual opening of the wastegate valve even when identical operation amounts are applied to an actuator that drives the wastegate valve, and a difference may occur in the actual supercharging pressure even when the actual opening of the wastegate valve remains constant. When such differences occur, it becomes impossible to realize the desired supercharging pressure.
Hence, to solve this problem, a technique of learning a deviation in a fully closed position of the wastegate valve, which is one of the main causes of these differences, has been proposed.
More specifically, a method of controlling the supercharging pressure by calculating a target supercharging pressure and a base opening of the wastegate valve for realizing the target supercharging pressure in accordance with the operating conditions of the internal combustion engine, calculating an opening correction amount on the basis of a deviation between the target supercharging pressure and the actual supercharging pressure, and feedback-controlling driving of the actuator so that the actual opening of the wastegate valve matches the target opening has been proposed (see Japanese Patent Publication No. 4434057, for example).
Further, to solve the problem described above, Japanese Patent Publication No. 4434057 discloses learning the fully closed position of the wastegate valve on the basis of the opening correction amount on condition that the internal combustion engine is warm, and indicates that by learning the fully closed position in this manner, a deviation in the fully closed position of the wastegate valve can be corrected, with the result that the desired supercharging pressure can be realized.
Furthermore, a method of controlling the supercharging pressure by calculating the target opening of the wastegate valve in accordance with the operating conditions of the internal combustion engine and feedback-controlling driving of the actuator so that the actual opening of the wastegate valve matches the target opening has been proposed (see Japanese Patent Application Publication No. 2015-59549, for example).
Moreover, to solve the problem described above, Japanese Patent Application Publication No. 2015-59549 discloses controlling the wastegate valve to the fully closed position initially when the target opening is the fully closed position, and then determining whether or not the wastegate valve has converged on the fully closed position on the basis of whether or not the actual opening of the wastegate valve is fluctuating about a fixed value in the vicinity of the fully closed position.
Next, Japanese Patent Application Publication No. 2015-59549 discloses learning the fully closed position of the wastegate valve on the basis of the output of the position sensor at this time, and correcting the fully closed position in accordance with temperature variation following the point at which the fully closed position is learned. Japanese Patent Application Publication No. 2015-59549 indicates that by learning and correcting the fully closed position in this manner, a deviation in the fully closed position of the wastegate valve can be corrected, with the result that the desired supercharging pressure can be realized.